Host-Busters

For those who manage multi-instance environments, providing a descriptive identifier, i.e. a hostname, to each node on a network may be of some utility. Once you've developed a naming convention that makes sense for you, here's a Bash script that will automate the renaming process on Debian-based systems:

#!/usr/bin/env bash
# Change hostname in Debian-based operating systems (OSs). 

# Assign existing hostname to $hostn

currenthost=$(cat /etc/hostname)

# Exit if not ROOT. 

root_user_check () {
  if [ "$EUID" != "0" ]; then 
    printf "%s\n" "ROOT privileges are required to continue. Exiting.">&2
    exit 1
fi 
} 

# Display existing hostname

show_current_hostname () {
  printf "%s\n" "Existing hostname is $currenthost"
}

# Ask for new hostname $newhost

get_new_hostname () { 
  printf "%s\n" "Enter new hostname: "
  read -r newhost
} 

# Change hostname in /etc/hosts & /etc/hostname

change_hostname () { 
  sed --in-place "s/$currenthost/$newhost/g" /etc/hosts
  sed --in-place "s/$currenthost/$newhost/g" /etc/hostname
} 

# Display new hostname

show_new_hostname () { 
  printf "%s\n" "Your new hostname is $newhost"
} 

# Press a key to reboot

rebooty () { 
  read -s -n 1 -rp "Press any key to reboot"
  reboot  
}  

# Main 

root_user_check

main () { 
  show_current_hostname 
  get_new_hostname 
  change_hostname
  show_new_hostname 
  rebooty     
} 

main "$@"

.

This script works well for already-provisioned instances, but what if you want to implement your naming convention when spinning up a new node (or several)? Well, you could use a service like CloudInit, which handles the "early initialization of a cloud instance." The same process then, using cloud-init:

#cloud-config 
runcmd: 
  - newhost="<%newhostname%>"
  - oldhost=$(cat /etc/hostname)
  - echo "Exisitng hostname is $oldhost"
  - echo "New hostname will be $newhost"
  - sed -i "s/$oldhost/$newhost/g" /etc/hosts
  - sed -i "s/$oldhost/$newhost/g" /etc/hostname
power_state: 
mode: reboot

.

Please note: the first script should end with .sh , like: change_host.sh. Make it executable with: chmod u+x change_host.sh, and run it with: ./change_host.sh. The second script needs to end in .yml, e.g.: change_host.yml.

If you'd like a TUI version of this script here you go.

Cheers.